Use unittest.mock instead of mock

The mock third party library was needed for mock support in py2
runtimes. Since we now only support py36 and later, we can use the
standard lib unittest.mock module instead.

Change-Id: Iabd3e90a46fd087c8e780796e04fcc050c5277ab

container_config_scripts/tests/test_nova_statedir_ownership.py

@@ -13,8 +13,9 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+from unittest import mock
+
 import contextlib
-import mock
 import six
 import stat
 import sys

lower-constraints.txt

@@ -51,7 +51,6 @@ Mako==0.4.0
 MarkupSafe==1.0
 mistral-lib==0.3.0
 mistral==6.0.0
-mock==2.0.0
 monotonic==0.6
 mox3==0.20.0
 msgpack-python==0.4.0

test-requirements.txt

@@ -14,7 +14,6 @@ python-subunit>=1.0.0 # Apache-2.0/BSD
 testrepository>=0.0.18 # Apache-2.0/BSD
 testscenarios>=0.4 # Apache-2.0/BSD
 testtools>=2.2.0 # MIT
-mock>=2.0.0 # BSD
 oslotest>=3.2.0 # Apache-2.0
 yaql>=1.1.3 # Apache 2.0 License
 ansible-runner>=1.4.2 # Apache

tripleo_heat_templates/tests/test_environment_generator.py

@@ -14,8 +14,8 @@
 
 import io
 import tempfile
+from unittest import mock
 
-import mock
 from oslotest import base
 import six
 import testscenarios